FIG. 1 shows a conventional electrical junction box 100 recited in Patent Document 1, for example, which is formed by assembling an insulation case 110 and an electrical component attachment block 120 together.
The insulation case 110 includes a housing 130 for housing the electrical component attachment block 120. A top and a bottom of the housing 130 are open, and the electrical component attachment block can 120 be inserted from either of upper and lower directions. First lock protrusions 140 and second lock protrusions 150 are formed on inner walls of the housing 130, and are configured to engage with the electrical component attachment block 120.
The electrical component attachment block 120 includes a block main body 180 inside which a conductor bus bar (whose illustration is omitted) is provided. The electrical component attachment block 120 electrically connects a power source to in-vehicle loads via the conductor bus bar. First lock arms 160 and second lock arms 170 are formed on outer surfaces of the block main body 180. The first lock arms 160 correspond to the first lock protrusions 140 on the insulation case 110, while the second lock arms 170 correspond to the second lock protrusions 150 on the insulation case 110. The first lock arms 160 are configured to engage with the first lock protrusions 140 when the electrical component attachment block 120 is inserted from above into the insulation case 110, while the second lock arms 170 are configured to engage with the second lock protrusions 150 when the electrical component attachment block 120 is inserted from below into the insulation case 110. That is to say, the first lock protrusions 140, the second lock protrusions 150, the first lock arms 160, and the second lock arms 170 collectively constitute a lock mechanism for assembling the electrical junction box 100.